Some Basic Concepts of Energy

Some Basic Conceptsof Energy III. Room heating and biological dimensions Prepared for BIO/EES 105 Energy in our World Kenneth M. Klemow, Ph.D. Wilkes University

Energy consumption – thermal comfort • Indoor environments often more comfortable than outdoor. • Stay dry • Regulate light • Regulate temperature • People prefer temperatures between 65-75oF • When T<65, we heat • When T>75, we cool

Focus on Keeping Warm • When cold we add heat via radiators, fireplaces, space heaters • Heat generators warm the air via radiant energy • If air carried away, need to warm the new air. • Energy needed = 0.018 BTU / ft3 / oF

Problem • Imagine you come upon a small, uninhabited, single-roomed cabin in the winter • Height = 10’ • Width = 20’ • Length = 20’ • It’s 15oF outside, you want to heat it to 65oF. • How many BTUs will it take?

Problem 2 • If energy costs $30.00 / million BTUs, how much will initially heating the cabin cost?

Keeping the cabin warm will be a challenge • Heat losses due to conduction through the walls. • Heat losses due to infiltration of cold air.

Look at conductive heat loss first • Building has four walls, a ceiling, and a floor • Heat will be lost through each • Go back to formula Q/t = (k x A x DT)/d • k = thermal conductivity of wall / floor / ceiling • d = thickness • For building material, we don’t consider thermal conductivity, per se. • Instead we express as thermal resistance (R value), where R = d/k. • Units = ft2-hr-oF/Btu

R values of different materials

Formula now converts to • Remember R = d/k • So 1/R = k/d • Remember Q/t = (k x A x DT)/d • So Q/t = k/d (A x DT) • And then 1/R (A x DT) • And then Q = 1/R (A x DT x t) Q = 1/R (A x DT x t) http://www.kfiam640.com/

Problem • How much energy (in BTU) is lost through a wall measuring 20’ x 10’ in an hour. • Assume: • Wall covered by 0.5” plywood • It’s 65oF inside and 15oF outside • How much energy is lost over the course of 24 hours?

Next problem • How much energy (in BTU) is lost from the entire house by conduction in an hour? • Hint 1: Calculate loss through the four walls • Hint 2: Calculate loss through the ceiling • Hint 3: Calculate loss through the floor • Hint 4: Add together • Then calculate loss from the house in a 24 hour day.

Now calculate cost • What is daily cost to heat house if energy = $30.00 / million BTUs? • What would be the monthly cost?

Effect of adding insulation • Go back to case of wall. How much heat was lost in an hour when wall was 0.5” plywood? • Now suppose that your wall was composed of 3.5” of fiberglass insulation. • Hint 1: Find R value for 3.5” of fiberglass • Hint 2: Recalculate based on that value. • Express the difference here____________ • If wall was 0.5” plywood AND 3.5” insulation, add the two R values together. • Then recalculate

Now do for entire cabin. • What would be hourly loss if all four walls were covered by 3.5” insulation? • What would be hourly loss if ceiling was covered by asphalt shingle above plywood? • What would be hourly loss if floor covered by 0.75” hardwood floor? • Next calculate over course of a day • Next calculate over course of a month

Air infiltration • Premise • Houses leak warm air, and allow cold air to enter • That air needs to be warmed up. • Formula for calculating this: Qinfil = 0.018 x V x KDT x t

Go back to our cabin • What would be energy loss in an hour, if all of the air is exchanged over the course of an hour? • How much energy would be lost over the course of 24 hours? • How much energy would be lost if the house leaked air at 1/10 the rate?

Total loss equal conductive and leakage added together. • Basis for home energy audit!

Terminology pertaining to modern energy • Renewable vs nonrenewable • Traditional vs new energy • Commercialized vs non-commercialized • Centralized vs distributed generation • On-grid vs off-grid

Stages of energy flowfrom http://www.fao.org/docrep/u2246e/u2246e02.htm • Primary energy is the energy as it is available in the natural environment, i.e. the primary source of energy. • Secondary energy is the energy ready for transport or transmission. • Final energy is the energy which the consumer buys or receives. • Useful energy is the energy which is an input in an end-use application.

Stages of energy flowfrom http://www.fao.org/docrep/u2246e/u2246e02.htm

Energy Carbon reduction CO2 C6H12O6 H2O Carbon oxidation Energy Why is living matter a source of energy?

In an organism, some energy is saved in its body as organic molecules. The rest is respired. Energy Respired Energy consumed Energy Stored

Ecosystems are comprised of different trophic levels

Energy flows through ecosystems Energy lost at each step (usually 90%)

Some Basic Concepts of Energy